It's not like your central nervous system just shuts down instantly with the moment of death. Your muscles will twitch, your heart will still pump blood, your eyes might look around the room for thirty seconds or so. Just because headquarters isn't processing the telegrams doesn't mean the outposts stop sending them.

Typically, people who commit suicide with a semi-automatic firearm will get at least two, if not three or four, shots off. Hemingway took two shot gun blasts. A guy in Germany actually shot his neighbor who burst into the room several seconds after the initial gunshot, killing them both. Your body will continue to do whatever it was doing before you shut off the brain.

This is why it's getting more and more popular in suicide clubs and death-fetish circles to masturbate during suicide. The hand stimulating the genitally will continue for some time, perhaps even to orgasm, though no one will be around to enjoy it. If you Google "suicide masturbation" you'll find plenty of self-shot videos of people orgasming all over their stomachs with half their head missing. The members of the suicide clubs consider the people who achieve postmortem release as "life's winners." I suppose it's winning if the game is see who can most fill their belly button with their own brains and come. I'll stick to breath control play and keyboard cleaner, thanks.